The present invention relates generally to reinforced cementitious panels or boards, and, in particular, cementitious panels or boards that are reinforced with a fabric that is unaffected by alkali attack.
The use of reinforced cement panels is well known in such industries as the ceramic tile industry. Generally, cement panels or boards contain a core formed of a cementitious material that is interposed between two layers of facing material. The facing materials employed typically share the features of high strength, high modulus of elasticity, and light weight so as to contribute flexural and impact strength to the high compressive strength but brittle material forming the cementitious core. Typically, the facing material employed with cement panels is fiberglass. Fiberglass performs particularly well in this application. Fiberglass provides greater physical and mechanical properties to the cement board. Fiberglass is also an efficient material to reinforce the cement panels because of its relatively low cost when compared with other high modulus materials.
Fiberglass, however, has a major disadvantage, which is its lack of resistance to chemical attack from the ingredients of the cements. Common cements, such as Portland cement, provide an alkaline environment when in contact with water, and the fiberglass yarn that is used in reinforcement fabrics is degraded in these highly alkaline conditions. To overcome this problem, protective polymeric coatings, such as PVC (polyvinyl chloride) plastisol coatings, are applied to the fiberglass. Although these coatings minimize fiberglass degradation, the protective coating on the fiberglass yarns is very critical to the success of the concrete panel. Even with a PVC coating, any imperfections in the coating allow sites for alkali attacks, which is accelerated with heat during the curing phase of the cementitious boards. Therefore, excess fiberglass must be included to ensure a minimum amount of strength over the life of the cement boards.
Accordingly, there remains a need for an improved cement panel that is reinforced by a fabric that both minimizes or eliminates the need to include a protective fabric coating and that retains the beneficial features of other facing materials.